1. Field of the Invention
The present invention relates to apparatus for minimizing fluid leakage between the rotating shaft and the stationary members in turbo-machinery such as turbines, compressors and the like. More particularly the invention relates to an improvement in a high pressure shaft seal of the type where the seal is prevented from rotating relative to the shaft.
2. Description of the Prior Art
In many high speed, high pressure machine applications, as for example those encountered in the turbine and compressor arts, the rotary components of the machine are mounted upon a shaft and the shaft is journaled for rotation within an opening formed for example in the end wall of a pressurized casing. Shaft seals are typically positioned within the casing opening to prevent pressurized fluid from escaping from high pressure regions to low pressure regions.
Non-rotating shaft seals are generally mounted within stationary components of the rotary machine with the opposed surfaces of the seals and components being in spaced apart relation. In conventional arrangements, for example, a pin is positioned between the seal and stationary portions of the compressor to prevent rotation of the seals. The pin is preferably press fitted into the stationary component, such as a seal stator element, for preventing the seal from rotating with the shaft. Although this pin connection does not allow the shaft seal to rotate, the connection is such that the shaft seal is permitted to move in a radial direction relative to the shaft. This is achieved by freely positioning the pin within a notch formed in the stationary element.
Shaft seals of the above described type are employed in turbomachines operating at relatively high pressure levels. Many of such machines are employed in applications requiring variable operating pressures. The radial movement of the shaft at high operating speeds and pressures produces a concomitant radial movement of the shaft seal. During prolonged use of the machine, the movement of the seal and pin, relative to the notch, results in the top surface of the pin gouging a channel or groove in the surrounding notch as the pin is forced into contact with a sidewall of the notch. At high speed and pressure condition, whereat relatively large radial shaft deflections are encountered, it has been found that the pin may become bound within the gouged channel. If the pin becomes bound, it may break due to the high load imposed upon the seal by the shaft. In addition, the seal surface encompassing the shaft will wear at a rapid rate since the seal cannot move radially once the pin is bound in the channel. Thus radial movement of the shaft into contact with the seal will eliminate the oil film normally found between the seal and shaft, thereby producing high shaft vibration and rapid wearing of the seal. These conditions are detrimental to the turbomachine's performance.